For the purpose of avoiding situations in which a user who uses a fake body and pretends to be an authenticated person is mistakenly authenticated as the proper authenticated person, a technique for judging whether a subject used in a biometric authentication process is a living body or a fake body is conventionally known (see, for example Japanese Laid-open Patent Publication No. 2007-244712).
More specifically, as depicted in FIG. 19, when an authenticated person is registered, a biometric information value of the authenticated person is measured, and a biometric information value range is specified so that a subject exhibiting a value that deviates from the measured biometric information value by an amount equal to or smaller than a predetermined amount is judged to be a living body. With this arrangement, when the biometric information value of a subject is within the biometric information value range, the subject is judged to be a living body.
The conventional technique described above, however, has a problem where, if the biometric information value of the authenticated person has fluctuated, even if an authentication process is performed on the authenticated person himself/herself, he/she may be judged to be a fake body. For example, according to the conventional technique described above, as depicted in FIG. 20, if the biometric information value of an authenticated person has gradually increased over the course of time and has become larger than the upper limit value of the biometric information value range used in the judgment process for fake body, a problem arises where, even if a biometric authentication process is performed on the authenticated person himself/herself, he/she will be judged to be a fake body.